Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jul. 02, 2023	Jul. 03, 2022	Jul. 02, 2023	Jul. 03, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 60,238	$ 58,657	$ 219,794	$ 180,205
Other comprehensive income, net of tax
Foreign currency translation adjustment, net of tax	44,500	(44,884)	69,453	(42,763)
Gain (loss) on cash flow hedge valuations, net of tax	(1,044)	2,380	(2,029)	9,984
Net pension adjustments	0	0	2,794	0
Other comprehensive income (loss), net of tax	43,456	(42,504)	70,218	(32,779)
Comprehensive income, net of tax	103,694	16,153	290,012	147,426
Comprehensive income attributable to noncontrolling interests, net of tax	4	6	23	25
Comprehensive income attributable to Tetra Tech, net of tax	$ 103,690	$ 16,147	$ 289,989	$ 147,401